Granite discovered on Mars, created over billions of years in volcanoes

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It might sound superficial, but for a long time Mars was judged for being too bland. A seemingly motionless expanse of homogenous rock, Mars as a planet was thought to be far less complex than something like Earth. With our oceans, our wonderful and destructive tectonic plates, and a few billion years of life’s tendency to change whole strata, we were definitely the more interesting planet, geologically.

New evidence might be calling that assumption into question, however, as a new spectrographic survey has found evidence for granite-like rocks on the surface of Mars. On Earth, granite is formed usually in tectonic subduction zones and other areas of plate movement; these provide the heat and stress necessary to form granite. The process takes millions of years and very specific circumstances, and while there is now evidence that Mars has tectonic plates much like Earth’s, it’s still unlikely it could form granite in this traditional way.

A shot of the Martian surface from the Mars Reconnaissance Orbiter.

When the rover Curiosity reported finding traces of granite, it was thus met with both bewilderment and skepticism. Where could granite come from on Mars? Those earlier findings provoked some controversy, since granite is not a rock you’d expect that Mars would be able to form. Now, spectroscopy can provide an alternate possible origin for granite on Mars: volcanoes.

Mars doesn’t have nearly the same level of volcanic activity as Earth. Being intermediate in size between the Earth and our Moon, it shows a similarly intermediate amount of activity. Still, some of its volcanoes seem to have been sporadically active for billions of years — long enough, perhaps, to make granite. The researchers managed to find a Martian volcano not shrouded in the planet’s trademark dust, and looked at light reflecting off its surface and the surrounding area. They found evidence of granite-like rocks.

As magma cools in the subsurface of Mars, it undergoes a process called fractionation, in which different components of the molten rock separate out based on density. Thus, denser crystals collect at the bottom, lighter materials at the top. On a long enough time-line, this process could lead to something like granite, though it is in fact an alien rock with properties all its own.